1. Field of the Invention
This invention relates to a method for growing a Group III nitride semiconductor crystal and a growing device for a Group III nitride semiconductor crystal.
2. Description of the Background Art
A nitride aluminum (AlN) crystal, which has a wide energy band gap of 6.2 eV, a high thermal conductivity of about 3.3 WK−1 cm−1 and high electrical resistance, has drawn public attentions as a substrate material for semiconductor devices, such as optical devices and electronic devices.
For example, a sublimation method is used as the method for growing a Group III nitride semiconductor crystal such as an AlN crystal. With respect to the method for growing AlN crystal, a method has been proposed in which the crystal is grown on a silicon carbide (SiC) substrate by using the sublimation method, for example, by the following Patent Documents: Japanese Patent Laying-Open No. 10-53495 (Patent Document 1), Specification of U.S. Pat. No. 5,858,086 (Patent Document 2), and Specification of U.S. Pat. No. 6,296,956 (Patent Document 3).
The above Patent Document 1 describes the following steps to be carried out. That is, first, by mixing AlN powder, titanium oxide (TiO2) that reacts with AlN under heat to decompose and evaporate AlN, and phenol with one another, a mixed powder is prepared. Moreover, a SiC substrate is prepared as a base substrate. Next, the resulting mixed powder is heated to 1800° C. in an atmosphere containing carbon and nitrogen, and at the same time, the SiC substrate is heated to 1700° C., and the mixed powder is consequently decomposed and evaporated so that an AlN crystal is grown over the SiC substrate.
Moreover, the above Patent Documents 2 and 3 describe a method in which a material is sublimated by using the sublimation method so that an AlN crystal is grown over a base substrate at a growing rate of 0.5 mm/hr.
In Patent Document 1, since the heating temperature of the material is as low as 1800° C., the rate of sublimation of the material becomes low. Therefore, there is a problem that the growing rate of AlN to be grown on the base substrate is low.
Moreover, in order to attain the growing rate of 0.5 mm/hr as described in Patent Documents 2 and 3, the material needs to be heated to a high temperature. However, an attempt to heat the material to a high temperature causes a high temperature of the base substrate. When the heating temperature of the base substrate becomes higher, the AlN crystal grown over the base substrate is re-sublimated, with the result that a problem arises in which the growing rate of the AlN crystal becomes insufficient.